1. Field of the Invention
This invention relates to zoom lens operating mechanisms for a zoom lens of a camera, such as a video or a still or movie photographic camera, and, more particularly, to an operating mechanism for a zoom lens to provide a focusing effect which varies continuously between a zoom effect and a close-up effect.
2. Description of the Prior Art
An operating mechanism for a zoom lens and which provides a focusing effect which varies continuously between a zoom effect and a close-up effect is known, and will now be described with reference to FIGS. 1 to 3 of the accompanying drawings.
In the known operating mechanism a plurality of guide rods 2 are arranged inside a stationary cylinder 1. A holding member 5 holding a variable lens group 3 (which may be a single lens) and another holding member 6 holding a correction lens group 4 (which may be a single lens) are mounted on the guide rods 2 such that the holding members 5 and 6 are both slidable in the direction indicated by arrows a and b.
A cam cylinder 7 is rotatably mounted inside the stationary cylinder 1. Two cam grooves 7a and 7b are formed in the inner wall of the cam cylinder 7, and FIG. 3 shows a developed view of a part of the cam cylinder 7 including the cam grooves 7a and 7b. A pin 5a formed on the holding member 5 is received in the cam groove 7a, and a pin 6a formed on the holding member 6 is received in the cam groove 7b.
An operating ring 8 is rotatably mounted on the outside of the stationary cylinder 1. A pin 7c extends radially outward from the cam cylinder 7 and engages with a recess 8a formed in the inner surface of the operating ring 8 through an elongated circumferential guide slot 1a formed in the stationary cylinder 1. When the operating ring 8 is rotated, the pin 7c moves along with the elongated guide slot 1a, and so the cam cylinder 7 is rotated with the operating ring 8.
An integral cylindrical portion 8b extends radially outward from the operating ring 8, and a pin-like operating member 9 having an end button 9a is disposed to extend through the cylindrical portion 8b of the operating ring 8. The operating member 9 is biased by a spring 10 in the radially inward direction as indicated by an arrow c.
A guide groove 1b is formed on the outer surface of the stationary cylinder 1 to extend circumferentially over a predetermined angle .alpha. as shown in FIG. 2. The inner end of the operating member 9 which is biased inward in the manner described above fits into the guide groove 1b.
A rotatable cylinder 12 holds a focusing lens 11 at the front end of the zoom lens, and a stationary cylinder 14 holds a relay lens 13 at the rear end of the zoom lens. A calibrated ring 15 is fixed on the stationary cylinder 1 and cooperates with a mark or marks on the rotatable cylinder 12.
With the operating mechanism described above, when the operating ring 8 is rotated to rotate the cam cylinder 7, the pins 5a and 6a of the holding members 5 and 6 move within the grooves 7a and 7b, respectively. Thus, the holding members 5 and 6 move along the guide rods 2 in the directions indicated by the arrows a and b so as to move the lens groups 3 and 4, respectively.
The displacement of the lens groups 3 and 4 is normally limited to a distance corresponding to the rotation of the operating ring 8 through the angle .alpha., that is, to an extent corresponding to the allowable movement of the operating member 9 along the guide groove 1b. Zoom photography may be performed within this angular range.
Additionally, however, the button 9a can be pulled in the direction indicated by an arrow d against the biasing force of the spring 10 when at the terminal end position for zoom photography where the operating member 9 abuts against the end of the guide groove 1b, whereupon the operating member 9 is disengaged from the guide groove 1b. The operating ring 8 can then be further rotated in the clockwise direction in FIG. 2 from this position. This further clockwise rotational movement of the operating ring 8 extends through another predetermined angle .beta., and within this angular range close-up photography may be performed.
When the operating ring 8 is rotated in the reverse direction for changing from the close-up mode to the zoom mode, the operating member 9 is automatically biased by the spring 10 in the direction indicated by the arrow c in FIG. 1 or 2, so that the inner end of the operating member 9 reenters the guide groove 1b at the transition to the zoom mode.
With this operating mechanism, the change from the zoom mode to the close-up mode is made merely by continuously rotating the operating ring 8. However, the change from the zoom mode to the close-up mode is marked by the temporary locking of the operating ring 8 and the need to pull out the operating member 9, so an unintentional change will not be made.
This need to pull the operating member 9 does, however, lead to a problem, particularly in the case of video and movie cameras, and this is that the necessary pull tends to transmit a vibration or displacement to the camera, and the user must try to counter this by holding the camera steady with one hand while pulling the operating member 9 with the other hand.
Moreover, it may be necessary to move the fingers on the operating member 9 so as to grasp the button 9a when the mode is to be changed from the zoom mode to the close-up mode, and this makes the operation a little awkward.
In another known operating mechanism a button 9a is depressed for changing the mode, but this is less satisfactory due to the possibility of accidental depression.
In yet another known operating mechanism an operating ring 8 is temporarily rotated in the reverse direction during the change from the zoom mode to the close-up mode, but this is rather a complex mechanism.